In the description below, the terms “marking” and “embossing” take the following meanings.
“Marking” involves compressing some portions of a sheet including several plies of tissue paper by forming compacted zones and significantly reducing the ply's thickness in these zones without however forming corresponding salients on the opposite side. When several plies, in particular two plies, are “marked” jointly, they will be combined and joined.
A marked product includes compressed zones of lesser thickness consisting of the marking patterns of the product.
“Embossing” involves creating one or several superposed tissue paper plies, salients on a first side with corresponding troughs on the opposite side of the plies, while increasing the thickness of the ply or superposed plies. The salients and troughs so made constitute embossing patterns at the surface of the paper products. This technique as well allows joining of the plies.
Most of the paper napkins presently on the market are connected by embossing at the edges, with entailed thickness in the joined peripheral zones.
Among the table napkins recently appearing on the market, some are mechanically joined at the edges of the plies and exclusively by marking.
One of the marking procedures consists in moving two tissue paper plies between an engraved steel cylinder and a smooth mating steel cylinder, the engraved cylinder has salients most of the time in the form of tips at that portion of its surface corresponding to the napkin's edges. The compression applied by the cylinders suffices to join the plies. The resultant cut product includes, on one of its surfaces, edges having compressed or compacted portions wherein the thickness is substantively reduced. There is no corresponding salient on the other product side. These products are characterized by the lack of excess thickness. Their central zone is flat, without excess thickness at its center. They lack bulk and “touch”, however, which are desired properties for products used in wiping the skin.
Another marking technique to join the tissues' edges is described in the patent application WO 95/274290 A.
This technique consists in marking each side of the product by using two engraved cylinders each fitted with salient parts in the form of tips, the tips of one cylinder being configured tip-to-tip with the tips of the other cylinder. The two plies are therefore joined by marking and by the point pressure applied by the cylinders. The two outer product sides at these points are recessed inward the sheet at the points, each point on one side matching another point on the other side.
This procedure entails very high accuracy and rigorous control.
The presently manufactured products incur the same drawbacks as those described above relating to conventional marking, namely that they are flat in the central zone.
European Patent Application 0 674 990 A describes embossed, paper table napkins. This embossing procedure allows creating, over a portion of the surface of each ply constituting the product, salient patterns with corresponding troughs on the opposite ply sides. As a result, the product is an embossed one and of greater thickness.
In this prior art of the above European Patent Application 0 674 990 A, there are three possibilities: embossing only the napkin's edges, embossing the full surface of the napkin, and embossing the edges with other embossing points selected in the central part between the edges.
In the first mode, once they are folded into four panes, the napkins incur some asymmetry. When stacked and wrapped, the packs tend to warp. Moreover, the napkins' touch is unpleasant near the edges because of the asymmetric embossing salients.
In the second mode, it is difficult to implement the high compressions required to emboss the full napkin surface, and consequently the mechanical junction between the plies is degraded, while there is also loss of softness because of the full surface embossing.
The third mode is a compromise between the other two, resorting to selective distribution of the embossing points in the napkin's central portion.
However, the drawbacks are a combination of those cited in the first and second modes.
The solution proposed in this prior art application EP 0 674 990 A to circumvent these various drawbacks is a napkin with functional embossing comprising an edge embossing and a decorative embossing pattern situated at one of the folds opposite the edge embossing. An unembossed wiping surface remains. In fact, the napkin portions that constitute the inner folded edges are embossed in order that the product, once it has been folded, is of fairly constant thickness, thereby avoiding the warping problems of the stacked napkin packs.
Patent Application WO 94/12343 A discloses another joining technique at the edges of a cut product, such as a tissue. This technique includes junction by embossing and glueing, the ply junction being implemented by glueing the edges. However, the manufacture of such products is problematic the moment an adhesive is used. Moreover, the adhesive will stiffen the product.